The present invention relates to a method of forming a single-crystal silicon layer and a method of manufacturing a semiconductor device, and a semiconductor device. Specifically, the invention relates to methods suitable for manufacturing a semiconductor device such as an insulated gate field effect transistor using a single-crystal silicon layer grown epitaxially on an insulating substrate for an active region, and relates to such a semiconductor device.
A TFT (Thin Film Transistor) is a MOSFET (Metal-oxide-semiconductor field effect transistor) using a single-crystal silicon layer formed on a substrate. As is known in the conventional art, a TFT exhibits an electron mobility several times greater than a transistor utilizing a polysilicon layer, and is suitable for high speed operations (see the following references, R. P. Zingg et al, xe2x80x9cFirst MOS transistors on Insulator by Silicon Saturated Liquid Solution Epitaxyxe2x80x9d. IEEE ELECTRON DEVICE LETTERS. VOL. 13, NO. 5, MAY 1992 p294-6., Publication of Examined Japanese Patent Application No. Hei 4-57098, Masakiyo Matsumura, xe2x80x9cThin Film Transistor,xe2x80x9d OYO BUTURI, Vol. 65, No. 8 (1996) pp842-848).
There are five deposition methods for forming a single-crystal silicon layer for such a semiconductor element:
(1) growing single-crystal silicon through the decomposition of silane, dichlorosilane, trichlorosilane, silicon tetrachloride at a temperature of about 800-1200xc2x0 C. in a hydrogen atmosphere at pressures of 100-760 Torr.
(2) forming a silicon epitaxial layer on a single-crystal silicon substrate as a seed by the cooling of a solution of indium and silicon or a solution of indium, gallium and silicon heated to 920-930xc2x0 C., and then forming a silicon semiconductor layer thereon (see the following references: Reference 1, Soo Hong Lee, xe2x80x9cVERY-LOW-TEMPERATURE LIQUID-PHASE EPITAXIAL GROWTH OF SILICONxe2x80x9d. MATERIALS LETTERS. Vol. 9. No. 2,3 (January, 1990) pp53-56. Reference 2, R. Bergmann et al, xe2x80x9cMOS transistors with epitaxial Si, laterally grown over SiO2 by liquid phase epitaxy.xe2x80x9d J. Applied Physics A, vol. A54, no. 1 p. 103-5. Reference 3, R. P. Zingg et al, xe2x80x9cFirst MOS transistors on Insulator by Silicon Saturated Liquid Solution Epitaxy.xe2x80x9d IEEE ELECTRON DEVICE LETTERS. VOL. 13, NO. 5, MAY 1992 p294-6.).
(3) growing silicon epitaxially on a sapphire substrate (see Reference 4, G. A. Garcia, R. E. Reedy, and M. L. Burger, xe2x80x9cHigh-quality CMOS in thin (100 nm) silicon on sapphire,xe2x80x9d IEEE ELECTRON DEVICE LETTERS. VOL. 9, pp32-34, January 1988.).
(4) forming a silicon layer on an insulating layer by oxygen ion implantation (see Reference 5, K. Izumi, M. Doken, and H. Ariyoshtl, xe2x80x9cCMOS device fabrication on buried SiO2 layers formed by oxygen implantation into silicon,xe2x80x9d Electron. Lett., vol. 14, no. 18, pp593-594, August 1978.).
(5) forming a step on a quartz substrate and then forming thereon a polysilicon layer, which is then heated to 1400xc2x0 C. or higher by laser beams or a strip heater to form an epitaxial layer on the step formed on the quartz substrate as a seed (see the following references: Reference 6, Seijiro Furukawa, xe2x80x9cGraphoepitaxy,xe2x80x9d The Transactions of the Institute of Electronics, Information and Communication Engineers, Vol. 66, No. 5, pp486-489. (1983. May). Reference 7, Geis, M. W., et al.: xe2x80x9cCrystallographic orientation of silicon on an amorphous substrate using an artificial-relief grating and laser crystallizationxe2x80x9d, Appl. Phys. Letter, 35, 1, pp71-74 (July 1979). Reference 8, Geis, M. W., et al.: xe2x80x9cSilicon graphoepitaxyxe2x80x9d, Jpn. J. Appl. Phys., Suppl. 20-1 pp.39-42 (1981).).
According to already known methods, all of the energy required for chemical reactions/single crystal growth is supplied in the form of heat energy (supplied by heating). This causes a problem that the epitaxial-growth temperature cannot be reduced to temperatures considerably lower than about 800xc2x0 C., more particularly 700xc2x0 C. This prevents epitaxial growth on, for example, a substrate kept at low temperatures or development of a method for forming a silicon epitaxial layer on a large glass plate which has a relatively low strain point. On the other hand, the method of growing silicon on a step formed on a glass plate as a seed to start epitaxial growth cannot attain the uniform epitaxial growth of silicon at a low temperature.
The invention has been achieved to overcome the above-described shortcomings. An object of the invention is to provide a method of forming a single-crystal silicon layer and a method of manufacturing a semiconductor device, and a semiconductor device, capable of the uniform epitaxial growth of a silicon layer at a low temperature on a large glass substrate with a relatively low strain point to enable the formation of a high-speed semiconductor element of a large current density thereon.
A method of forming a single-crystal silicon layer of the invention involves the formation of a single-crystal silicon layer on a seeding layer made of a material having a lattice match with a single| crystal silicon layer by CAD (Chemical Vapor Deposition) using a catalyst.
Another method of forming a single-crystal silicon layer of the invention entails the formation of a single-crystal silicon layer on a single-crystal silicon substrate by CAD using a catalyst.
A method of manufacturing a semiconductor device of the invention includes the above-stated step of forming a single-crystal silicon layer, and a subsequent step of manufacturing a semiconductor element through a predetermined treatment of the single-crystal silicon layer.
A semiconductor device of the invention comprises: an insulating substrate; a seeding layer made of a material having a lattice match with single-crystal silicon, the seeding layer formed on the insulating substrate; a single-crystal silicon layer formed on the seeding layer, the single-crystal silicon layer forming a semiconductor element.
According to the present invention, single-crystal silicon is deposited (grown epitaxially) on a seeding layer made of a material having a lattice match with single-crystal silicon (for example, a crystalline sapphire layer) or a single-crystal silicon bulk substrate as a seed by CAD using a catalyst. This enables several outstanding effects and advantages to be obtained, which are as in the followings:
(A) the seeding layer as a seed to start silicon epitaxial growth can be formed by low-pressure CAD (CAD at a low pressure: where the temperature of the substrate is 500-600xc2x0 C.). In addition, on the seeding layer or a single-crystal silicon substrate, a single-crystal silicon layer can be formed by a low-temperature deposition method, that is, CAD using a catalyst (in which the temperature of the substrate is 100-700xc2x0 C. and preferably 200-600xc2x0 C.). This enables the uniform formation of a single-crystal silicon layer on a substrate at a low temperature. Especially, the seeding layer such as a crystalline sapphire layer or a single-crystal silicon substrate makes silicon epitaxial growth easy, having an excellent lattice match with single-crystal silicon particularly because of a lattice constant equal to that of single-crystal silicon.
(B) this makes it possible to use a substrate easily and cheaply available and made of a material of excellent properties, such as a glass substrate having a relatively low strain point, a ceramic substrate or a single-crystal silicon bulk substrate. Of course, a substrate made of quartz glass can be used. Besides, it becomes possible to use a substrate of long dimension more than 100 m or of larger surface area larger than 1 m2. This enables the formation of a continuous single-crystal silicon layer on a glass substrate in the form of a roll of wide and long dimensions.
(C) single-crystal silicon can be grown at low temperatures, preventing auto-doping of impurities to simplify the process (specifically, a step of sealing the back of a high-concentration substrate is no longer necessary).
(D) the quality of a silicon epitaxial layer can be improved. Specifically, a decrease in diffusion of impurities contributes to more precise control of the concentration and the thickness of a silicon epitaxial layer. Especially in the case of forming a silicon epitaxial layer on a sapphire substrate, strains caused by heat can be reduced, further suppressing auto-doping of aluminum.
(E) low substrate temperatures (100-700xc2x0 C. in CAD using a catalyst, 1000-1200xc2x0 C. in the conventional art) can reduce heating power requirements. Also, a cooling mechanism can be simplified, making a silicon epitaxy system cheaper.
(F) large reaction efficiency (several tens of percentage in CAD using a catalyst, a few percents or less in the conventional CAD) of reaction gases such as silane saves resources and has a low impact on the environment. This also contributes to a cost reduction.
(G) the seeding layer such as a crystalline sapphire layer also serves as a barrier to diffusion of various atoms, suppressing diffusion of impurities from a glass substrate or other substrates.
(H) the electron mobility in a single-crystal silicon layer formed on a glass substrate or others at a low temperature is as big as 540 cm2/vxc2x7sec (see Reference 3 above), which is equivalent to that of a single-crystal silicon substrate. Therefore, it becomes possible to fabricate a top-gate, bottom-gate or dual-gate TFT for a LCD (Liquid Crystal Display), which is high-speed and has a large current density, a transistor for an EL (Electro luminescence) or a FED (Field Emission Display), a high-performance semiconductor element such as a diode, a solar cell, a capacitor or a resistor and the like, or integrated circuits on a glass substrate.
Other objects and advantages of the present invention will become apparent from reading the following detailed description and appended claims, and upon reference to the accompanying drawings.